1. Field of the Invention
This invention relates to the field of explosive compositions, especially compositions useful for thermobaric weapons, and further relates to thermobaric weapons and methods for making and deploying the same.
2. Description of the Related Art
Thermobaric explosives (TBX) are a class of volumetric weaponry designed to produce heat and pressure effects. Thermobaric explosives are generally fuel-rich (e.g., aluminum rich) compositions usually containing a nitramine or other oxidizer or energetic, and are characterized by an energy release occurring over a longer period of time than standard explosives.
FIG. 3 is a graph comparing the pressure pulse of a thermobaric explosive (TBE) to that of a high explosive (HE). In the graph, a high explosive (HE) and thermobaric explosive (TBE) are detonated at time to, creating respective pressure pulses. The peak overpressure (PHE) of the initial pressure pulse of the high explosive is much greater than the corresponding peak overpressure (PTBE) of the initial pressure pulse of the thermobaric explosive. However, the initial pressure pulse generated by a high explosive is typically much shorter in duration than the corresponding pressure pulse of a thermobaric explosive (TBE). The overpressure generated by the high explosive drops at a much faster rate, passing below ambient pressure at time tHE. In contrast, although the thermobaric explosive has a lower initial peak overpressure PTBE in FIG. 3, the initial pressure pulse of the thermobaric explosive continues in duration until tTBE. As a consequence of the extended duration of the thermobaric explosive initial pressure pulse, the total impulse generated by the thermobaric explosive (represented graphically by the area between the TBE curve and ambient pressure between times t0-tTBE) is greater than the total impulse of the high explosive.
Without necessarily wishing to be bound by a particular theory, it is believed that the thermobaric explosive undergoes the following stages upon detonation. In a first overpressure stage, an initial shock (or blast) wave upon detonation of the explosive causes the nitramine to undergo anaerobic detonation in an essentially reduction-oxidization (redox) reaction occurring within hundreds of microseconds to disperse an expanding cloud of the flammable aluminum fuel particles into the surrounding air. This blast wave consumes most of the nitramine. Any remaining nitramine will contribute to an anaerobic combustion or dispersion of the fuel particles. The amount of fuel burned in this anaerobic reaction may be considered negligible. The cloud of fuel-rich energetic material is subject to aerobic combustion, which results from dispersed aluminum fuel particles in the shock wave mixing with oxygen in the surrounding air to produce a mammoth fireball that may last up to several seconds. The total impulse released in this first overpressure stage may be sufficient to flatten a building or penetrate deeply into complex and entrenched structures, such as caves and multi-room buildings.
After the first overpressure stage has ended, i.e., at time tTBE until a vacuum is left behind in the area in which the thermobaric explosive has been detonated. This vacuum draws in close objects, including unexploded fuel particles that create almost complete penetration into all non-airtight objects within the blast radius, which are then incinerated. A second overpressure stage begins at time t5. However, the impulse created in this second overpressure stage is negligible compared to the first overpressure stage for the purposes of this description, and is not discussed further herein.
It is desirable to increase the total impulse generated by a thermobaric weapon during the initial pressure pulse. An increased impulse would improve the destructive force of the explosive, for example, in the leveling of a reinforced building or the penetration of particularly deep or windy caves or multi-room structures. Theoretically, raising the peak overpressure (PTBE) or prolonging the duration (tTBE) of the initial pressure pulse should increase the impulse of the thermobaric weapon.
It has been found that raising the concentration of aluminum fuel particles beyond about 35 weight percent of the total weight of the thermobaric explosive does not significantly increase the initial impulse of the explosion. Aluminum fuel particles require oxygen for combustion. The oxygen available for aerobic combustion of the aluminum fuel particles is limited to the oxygen present in ambient air in close proximity to the detonation site, and more specifically to the oxygen in ambient air that comes into contact with the dispersed aluminum. The aluminum particles deplete the available ambient-air oxygen. As a consequence, it has been considered wasteful to exceed a 35 weight percent loading of fuel particles in a thermobaric composition, because insufficient ambient-air oxygen is available to combust excess aluminum particles in the first overpressure reaction.
Non-combusted aluminum fuel particles do not contribute significantly to the initial pressure pulse and can account for size and weight penalties. More typically, the fuel particle load is closer to about 20 weight percent.
3. Objects of the Invention
It is an object of this invention to provide a thermobaric composition that undergoes a relatively long initial pressure pulse to increase the overall impulse generated by the composition during the initial pressure pulse.
It is another object of this invention to provide articles of manufacture, such as but not necessarily limited to warheads, bombs, projectiles, grenades and munitions comprising the thermobaric explosive of this invention.
It is yet another object of this invention to provide methods for making and deploying the thermobaric explosives and articles of manufacture of the present invention.